1. Field of Invention
This invention relates to surface treatment of polyolefin parts, in particular, to permanently bonding granular materials to surfaces of polyethylene parts such as containers and outdoor signs.
2. Brief Statement of the Prior Art
Polyolefin surfaces, particularly polyethylene surfaces, resist acceptance of coatings. These polymers are commonly used to form large, hollow-form parts such as outdoor signs, tanks and containers by rotational molding. The surfaces of these parts are smooth and difficult to coat.
In many instances, it is desirable to apply granular or particulate materials to the surfaces of such parts, e.g., containers which also function as steps need a roughened or abrasive texture and outdoor signs can be enhanced with reflective glass beads or microspheres.
U.S. Pat. No. 2,628,172 discloses a polyethylene dispersion which is coated onto a polyethylene surface and heated sufficiently to melt the coating, but not the polyethylene surface, to provide a coating with enhanced adhesion.
U.S. Pat. No. 5,840,142 discloses and claims a method for the permanent application of indica to the surface of a molded polyethylene part using a transfer which is screen printed with a wax, polyethylene and pigment mixture. After application to the surface of a polyethylene part, the transfer is coated with a mixture of polyethylene and wax and the part is heated to fuse the coating and transfer into the surface of the part. Unfortunately, the method of this patent cannot be used to create a part with a roughened or textured surface, since the method achieves complete integration of the applied coatings into the surface of the part, forming a smooth clear surface.